For development on bush fire prone land preliminary consideration of construction levels is necessary at the development application stage.
There are five categories of bush fire attack that are used to determine the appropriate level of construction to be applied to a development:
- Flame zone
The categories are determined by:
- The type of vegetation in your area
- How close your building is to the vegetation
- What the ground slope is, as fire runs more readily uphill. The risk is greater for a slope over 15 degrees.
The building requirements for house design and construction vary according to the category of bush fire attack that a development falls into.
The building requirements for each level of construction are set out in Australian Standard: 3959 (AS: 3959) and there are 3 levels of construction:
- Level 1 construction
- Level 2 construction
- Level 3 construction
Detailed below are the various categories and bush fire attack and the associated construction requirements
Minimal attack from radiant heat and flame due to the distance of the site from the vegetation, although some attack by burning debris is possible. There is insufficient threat to warrant specific construction requirements, but residents should still do basic property preparation.
Attack by burning debris is significant with radiant heat (not greater than 12.5kW/m2). Radiant heat is unlikely to threaten building elements (i.e. unscreened glass). Specific construction requirements for ember protection and accumulation of debris are warranted (Level 1 construction standards).
Attack by burning debris is significant with radiant heat levels (not greater than 19kW/m2) threatening some building elements. Specific construction requirements for embers and radiant heat are warranted (Level 2 construction standards).
Attack by burning debris is significant and radiant heat levels (not greater than 29kW/m2) threaten building integrity. Specific construction requirements for ember and higher radiant heat are warranted. Some flame contact is possible (Level 3 construction standards).
Radiant heat levels will exceed 29kW/m2, and radiant heat levels and flame contact are likely to significantly threaten building integrity and result in significant risk to residents who are unlikely to be adequately protected.
The flame zone is outside the scope of AS:3959 and the RFS will recommend protection measures in addition to minimum Level 3 construction.
Other measures such as sprinkler systems, radiant heat barriers and fire rated glass may also be required.
In preparing a development application under section 79BA, an applicant may consider the provision of higher-level construction standards as a level of equivalence for the inability to provide the required APZ. Consideration may also be given to additional measures such as drenching systems, radiant heat shields and shutters to satisfy the performance criteria.